"The Good German" is not successful because it is confusing.
First off the title is confused with Robert De Niro's flick, "The Good Shepard." This "Good German" is filmed in glorious black & white, but contains modern day motivations and language. Soderbergh can not decide whether it is a World War II romance or a film noir vehicle without expressionistic artistry. The last scene echoes "Casablanca" and some Stanley Kramer drama from the late fifties and early sixties, without a coherent theme.
The only certain thing that can be said about "The Good German" is that it is a time passer.